This invention relates to an ink jet recording head wherein a piezoelectric element is formed via a diaphragm in a part of each of pressure generating chambers communicating with nozzle orifices for jetting ink drops and ink drops are jetted by displacement of the piezoelectric element, and an ink jet recording apparatus comprising the ink jet recording head.
The following two types of ink jet recording heads, each wherein a part of a pressure generating chamber communicating with a nozzle orifice for jetting an ink drop is formed of a diaphragm and the diaphragm is deformed by a piezoelectric element for pressurizing ink in the pressure generating chamber for jetting an ink drop through the nozzle orifice, are commercially practical: One uses a piezoelectric actuator in a vertical vibration mode in which the piezoelectric element is expanded and contracted axially and the other uses a piezoelectric actuator in a deflection vibration mode.
With the former, the volume of the pressure generating chamber can be changed by abutting an end face of the piezoelectric element against the diaphragm and a head appropriate for high-density printing can be manufactured, but a difficult step of dividing the piezoelectric element like comb teeth matching the arrangement pitch of the nozzle orifices and work of positioning and fixing the piezoelectric element divisions in the pressure generating chambers are required and the manufacturing process is complicated.
In contrast, with the latter, the piezoelectric element can be created and attached to the diaphragm by executing a comparatively simple process of putting a green sheet of a piezoelectric material matching the form of the pressure generating chamber and baking it, but a reasonable area is required because deflection vibration is used; high-density arrangement is difficult to make.
On the other hand, to solve the problem of the latter recording head, Japanese Patent Publication No. 5-286131A proposes an art wherein an uniform piezoelectric material layer is formed over the entire surface of a diaphragm according to a film formation technique and is divided to a form corresponding to a pressure generating chamber according to a lithography technique for forming a piezoelectric element separately for each pressure generating chamber.
This eliminates the need for work of putting the piezoelectric element on the diaphragm and the piezoelectric element can be created by the lithography method, an accurate and simple technique. In addition, the piezoelectric element can be thinned and high-speed drive is enabled. In this case, with the piezoelectric material layer provided on the whole surface of the diaphragm, at least only upper electrodes are provided in a one-to-one correspondence with the pressure generating chambers, whereby the piezoelectric actuator corresponding to each pressure generating chamber can be driven.
In such an ink jet recording head, generally a reservoir which becomes an ink chamber common to pressure generating chambers is formed by depositing a plurality of substrates on each other, and ink is supplied from the reservoir to the pressure generating chambers. To hold the internal pressure of the reservoir constant, the reservoir is provided with a compliance section for absorbing pressure change when a piezoelectric element is driven.
However, a large number of substrates used to form the reservoir are required; particularly a large number of substrates deposited to form the compliance section are required, increasing material and assembly costs.
The ink jet recording head as described above is intended to have a large number of nozzles and it is necessary to form the reservoir in size capable of sufficiently supplying ink to the pressure generating chambers accordingly; the strength of the substrates forming the reservoir is degraded inevitably. Thus, if heat is applied to the substrates at an installation step, the substrates are warped due to thermal expansion and a crack occurs.
To use silicon for the substrate for defining each pressure generating chamber, it is difficult to bond at a high temperature because of the difference from other substrates in thermal expansion coefficient and the number of assembly steps is increased.
It is therefore an object of the invention to provide an ink jet recording head for preventing deformation and cracking of substrates with a structure simplified and manufacturing costs reduced, and an ink jet recording apparatus comprising the ink jet recording head.
In order to achieve the above object, according to a first aspect of the invention, there is provided an ink jet recording head comprising: a nozzle forming member provided with a plurality of nozzle orifices for jetting ink; a channel forming substrate provided with a plurality of pressure generating chambers communicated with the associated nozzle orifices, one face of which is bonded to the nozzle forming member; a plurality of piezoelectric elements provided on an face of the channel forming substrate which is opposed to the face bonded to the nozzle forming substrate with a vibration plate in between for changing the associated pressure generating chambers in volume thereof; and a reservoir forming member bonded to the face of the channel forming substrate on which the piezoelectric elements are provided, the reservoir forming member having a reservoir section forming at least a part of a reservoir communicated with the pressure generating chambers for supplying ink thereto, and a piezoelectric element holding section for defining a space in an area facing the piezoelectric elements such an extent that motion of the respective piezoelectric elements is exhibited while sealing the space hermetically.
In the first aspect, the number of substrates deposited for forming the reservoir can be reduced and the structure can be simplified. In addition, the piezoelectric elements are hermetically sealed in the piezoelectric element holding section and destruction of the piezoelectric elements caused by the external environment is prevented.
According to a second aspect of the invention, in the ink jet recording head in the first aspect, the piezoelectric element holding section is partitioned by partition walls so as to correspond to the respective piezoelectric elements and the partition walls are bonded to the channel forming substrate.
In the second aspect, the rigidity of the peripheral walls partitioning the pressure generating chambers is increased, and falling down of the peripheral walls when the piezoelectric element is driven is prevented.
According to a third aspect of the invention, in the ink jet recording head in the first or second aspect, the channel forming substrate is formed with a communication section for communicating with the reservoir section of the reservoir forming member to form a part of the reservoir together with the reservoir section.
In the third aspect, the reservoir is made up of the reservoir section and the communication section; a reservoir of a relatively large volume can be formed easily.
According to a fourth aspect of the invention, in the ink jet recording head in any of the first to third aspects, the reservoir and each pressure generating chamber are made to communicate with each other via an ink supply passage relatively narrower than the reservoir.
In the fourth aspect, ink is supplied from the reservoir to the pressure generating chamber via the ink supply port having a relatively narrower flow passage than the reservoir, so that the amount of bubbles mixed into the ink is suppressed.
According to a fifth aspect of the invention, in the ink jet recording head in any of the first to fourth aspects, an ink introduction port communicating with the outside for supplying ink to the reservoir is made to communicate with the reservoir section.
In the fifth aspect, ink is supplied through the ink introduction port to the reservoir.
According to a sixth aspect of the invention, in the ink jet recording head in any of the first to fifth aspects, the reservoir section is so formed as to be across the pressure generating chambers placed side by side.
In the sixth aspect, ink is supplied from the reservoir common to the pressure generating chambers.
According to a seventh aspect of the invention, in the ink jet recording head in any of the first to sixth aspects, a part of the reservoir section of the reservoir forming member has a flexible section having flexibility.
In the seventh aspect, change in the internal pressure of the reservoir is absorbed as the flexible section becomes deformed, whereby the inside of the reservoir is always held at a constant pressure.
According to an eighth aspect of the invention, in the ink jet recording head in the seventh aspect, the channel forming substrate in the area corresponding to the reservoir section is formed with a through section piercing the channel forming substrate without communicating with the pressure generating chambers. The flexible portion is defined as a section between the through section and the reservoir section.
In the eighth aspect, the flexible section placed between the through section and the reservoir section becomes elastically deformed, thereby absorbing pressure change in the reservoir for always holding the inside of the reservoir at a constant pressure.
According to a ninth aspect of the invention, in the ink jet recording head in the eighth aspect, the through section is so formed as to be across the pressure generating chambers placed side by side.
In the ninth aspect, the flexible section is formed in an area capable of sufficiently absorbing pressure change in the reservoir.
According to a tenth aspect of the invention, in the ink jet recording head in the eighth or ninth aspect, the through section is etched together with the pressure generating chambers and is formed.
In the tenth aspect, the flexible section can be formed relatively easily.
According to an eleventh aspect of the invention, in the ink jet recording head in any of the seventh to tenth aspects, the flexible section is provided by bonding a flexible member.
In the eleventh aspect, the flexible section can be easily provided by bonding a flexible member.
According to a twelfth aspect of the invention, in the ink jet recording head in the eleventh aspect, the flexible member is a thin film made of at least one of metal and ceramic.
In the twelfth aspect, a thin film is formed, whereby the flexible section can be easily formed.
According to a thirteenth aspect of the invention, in the ink jet recording head in the eleventh aspect, the flexible member is made of a resin material.
In the thirteenth aspect, the flexible section is made of a resin member and thus can be easily formed.
According to a fourteenth aspect of the invention, in the ink jet recording head in the thirteenth aspect, the resin material is at least one selected from the group consisting of fluororesin, silicone resin, and silicone rubber.
In the fourteenth aspect, a specific resin material is used, whereby the flexible section can be formed reliably.
According to a fifteenth aspect of the invention, in the ink jet recording head in the eleventh aspect, the flexible member contains a layer having a tensile stress.
In the fifteenth aspect, the flexible film is not buckled and can be prevented from being destroyed.
According to a sixteenth aspect of the invention, in the ink jet recording head in the eleventh aspect, the flexible member is composed of a layer forming the piezoelectric elements.
In the sixteenth aspect, when the piezoelectric elements are formed, the flexible member can be easily formed together with the piezoelectric elements.
According to a seventeenth aspect of the invention, in the ink jet recording head in any of the eleventh to sixteenth aspects, another substrate having a through hole at least in an area facing the flexible section is bonded to the flexible member.
In the seventeenth aspect, the strength of other portions than the flexible section is enhanced and the durability of the head is improved.
According to an eighteenth aspect of the invention, in the ink jet recording head in any of the eleventh to seventeenth aspects, a projected beam member is provided on the surface of the flexible member on the opposite side to the reservoir section so as to extend in a plane direction of the flexible member.
In the eighteenth aspect, the strength of the flexible film is increased by means of the beam member and the durability is improved.
According to a nineteenth aspect of the invention, in the ink jet recording head in the eighteenth aspect, the beam member is formed like a grid.
In the nineteenth aspect, the strength of the flexible film is increased by means of the grid-like beam member and the durability is improved.
According to a twentieth aspect of the invention, in the ink jet recording head in any of the first to nineteenth aspects, the reservoir section is provided with at least one beam-like reinforcing member across side walls defining the reservoir section and facing each other.
In the twentieth aspect, the rigidity of the reservoir section is enhanced by means of the reinforcing section and cracking of the reservoir forming member caused by a thermal stress at the installation time is prevented.
According to a twenty-first aspect of the invention, in the ink jet recording head in the twentieth aspect, at least a part of the reinforcing section is thinner than any other portion of the reservoir forming member.
In the twenty-first aspect, the rigidity of the reservoir section is improved without degrading the function of the reservoir.
According to a twenty-second aspect of the invention, in the ink jet recording head in the twenty-first aspect, at least a part of the reinforcing section on the side of the channel forming substrate is removed and is thinner than any other portion.
In the twenty-second aspect, the function of the reservoir can be maintained reliably and the rigidity of the reservoir section is -improved.
According to a twenty-third aspect of the invention, in the ink jet recording head in any of the twentieth to twenty-second aspects, the reinforcing section is formed along the longitudinal direction of the piezoelectric elements.
In the twenty-third aspect, cracking of the reservoir forming substrate caused by a thermal stress at the installation time is prevented reliably.
According to a twenty-fourth aspect of the invention, in the ink jet recording head in any of the first to twenty-third aspects, at least a part of the area of the reservoir forming member facing the piezoelectric element is formed with a detection through hole for detecting displacement of the piezoelectric element.
In the twenty-fourth aspect, displacement of the piezoelectric element can be detected easily from the outside of the reservoir forming member.
According to a twenty-fifth aspect of the invention, in the ink jet recording head in the twenty-fourth aspect, the piezoelectric element holding section is formed by piercing the reservoir forming member and is sealed with a transparent member, and also serves as the detection through hole.
In the twenty-fifth aspect, displacement of the piezoelectric element can be detected with the piezoelectric element hermetically sealed.
According to a twenty-sixth aspect of the invention, in the ink jet recording head in the twenty-fifth aspect, the transparent member forms the flexible section.
In the twenty-sixth aspect, change in the internal pressure of the piezoelectric element holding section is absorbed as the transparent member becomes deformed, whereby the internal pressure of the piezoelectric element holding section is held constant.
According to a twenty-seventh aspect of the invention, the ink jet recording head in any of the first to twenty-sixth aspects further comprises: a first wiring drawn out from the piezoelectric elements on the channel forming substrate; a second wiring provided on the reservoir forming member in an area opposite side of the channel forming substrate; a connection wiring for connecting the first and second wirings; and an external wiring connected to the second wiring.
In the twenty-seventh aspect, the wiring drawn out from the piezoelectric element and the external wiring are connected in the area of the reservoir forming member on the opposite side to the channel forming substrate, so that the head can be miniaturized.
According to a twenty-eighth aspect of the invention, in the ink jet recording head in the twenty-seventh aspect, the connection wiring is formed by wire bonding.
In the twenty-eighth aspect, the connection wiring can be formed easily.
According to a twenty-ninth aspect of the invention, in the ink jet recording head in the twenty-seventh aspect, the connection wiring is formed of a thin film.
In the twenty-ninth aspect, the connection wiring can be formed easily.
According to a thirtieth aspect of the invention, in the ink jet recording head in any of the twenty-seventh to twenty-ninth aspects, the reservoir forming member is formed with a communication hole piercing the reservoir forming member for communicating with the outside in the area corresponding to the piezoelectric element. The connection wiring is provided via the communication hole.
In the thirtieth aspect, the connection wiring can be placed in the reservoir forming member, so that the head can be miniaturized.
According to a thirty-first aspect of the invention, in the ink jet recording head in the thirtieth aspect, the communication hole is made in the area facing a peripheral wall of the pressure generating chamber on the reservoir side.
In the thirty-first aspect, the connection wiring is placed via the communication hole on the reservoir side.
According to a thirty-second aspect of the invention, in the ink jet recording head in the thirtieth aspect, the communication hole is made in the area facing a peripheral wall of the pressure generating chamber on the nozzle orifice side.
In the thirty-second aspect, the connection wiring is placed via the communication hole on the nozzle orifice side.
According to a thirty-third aspect of the invention, in the ink jet recording head in any of the twenty-seventh to thirty-second aspects, a drive circuit for driving the piezoelectric elements is mounted in the reservoir forming member. The connection wiring is connected to the drive circuit.
In the thirty-third aspect, the drive circuit can be mounted on the reservoir forming member for saving the space.
According to a thirty-fourth aspect of the invention, in the ink jet recording head in the thirty-third aspect, the drive circuit is a semiconductor integrated circuit.
In the thirty-fourth aspect, the drive circuit can be mounted easily on the reservoir forming member and space saving can be intended reliably.
According to a thirty-fifth aspect of the invention, in the ink jet recording head in any of the first to thirty-fourth aspects, the reservoir forming member is a reservoir forming substrate including the reservoir section.
In the thirty-fifth aspect, the ink jet recording head capable of reliably supplying ink to the pressure generating chambers through the reservoir can be realized easily.
According to a thirty-sixth aspect of the invention, in the ink jet recording head in the thirty-fifth aspect, the thermal expansion coefficient of the reservoir forming substrate is substantially the same as that of the channel forming substrate.
In the thirty-sixth aspect, it is made possible to bond the reservoir forming member and the channel forming substrate at a high temperature, and the manufacturing process can be simplified.
According to a thirty-seventh aspect of the invention, in the ink jet recording head in the thirty-fifth or thirty-sixth aspect, the reservoir forming substrate is made of at least one material selected from the group consisting of silicon, glass, and ceramics.
In the thirty-seventh aspect, the reservoir forming substrate is formed of a specific material, whereby the manufacturing process can be simplified reliably.
According to a thirty-eighth aspect of the invention, in the ink jet recording head in any of the first to thirty-seventh aspects, the nozzle forming member is formed of substantially the same material as the channel forming substrate and the reservoir forming member.
In the thirty-eighth aspect, joining of the nozzle forming member is facilitated and the manufacturing process can be simplified.
According to a thirty-ninth aspect of the invention, in the ink jet recording head in any of the first to thirty-eighth aspects, the nozzle forming member is a nozzle plate provided with the nozzle orifices.
In the thirty-ninth aspect, the ink jet recording head for jetting ink through the nozzle orifices can be realized easily.
According to a fortieth aspect of the invention, in the ink jet recording head in any of the first to thirty-ninth aspects, the pressure generating chambers are formed on a ceramic substrate. The layers of the piezoelectric element are formed by putting a green sheet or printing.
In the fortieth aspect, the head can be manufactured easily.
According to a forty-first aspect of the invention, in the ink jet recording head in any of the first to fortieth aspects, the pressure generating chambers are formed on a silicon monocrystalline substrate by anisotropic etching and the layers of the piezoelectric element are formed by thin film deposition and lithography method.
In the forty-first aspect, ink jet recording heads each having high-density nozzle orifices can be manufactured in large quantities and comparatively easily.
According to a forty-second aspect of the invention, there is provided an ink jet recording apparatus comprising an ink jet recording head in any of first to forty-first aspects.
In the forty-second aspect, an ink jet recording apparatus with the head structure simplified and manufacturing costs reduced can be realized.